The optimal treatment of superficial venous thrombosis (SVT) is still uncertain. Though low molecular weight heparin (LMWH) is considered the treatment of choice, studies conducted so far do not give clear indications of the optimal dose and duration of treatment. This study aims to evaluate whether an intermediate therapeutic dose of LMWH (parnaparin) is more effective than a prophylactic dose and also to assess whether 10 rather than 30 days are sufficient for treatment.

Outpatients with an episode of SVT of the grand saphenous vein (for at least 4 cm), and/or SVT of the small saphenous vein (for at least 4 cm), and/or SVT of a collateral vein of the large saphenous vein of the thigh (for at least 4cm) are included in this prospective, randomised, double blind, national multicentre study.

Patients will be randomised into double-blind groups to receive (syringes will be identical in appearance) in consecutively numbered boxes:

A - Parnaparin, dose of 8,500 IU aXa taken subcutaneously once a day for 10 days B - Parnaparin, dose of 8,500 IU aXa per day for 10 days followed by Parnaparin 6,400 IU aXa per day for the subsequent three weeks. C - Parnaparin, dose of 4,250 IU aXa per day for 30 days Elastic compression treatment will be recommended with special stocking and/or elastic bandaging with compression to the ankles of 20-40 mmHg, where not contraindicated.

Inclusion Criteria:

• Weight > 50 kg and less than 110 kg
• SVT of the grand saphenous vein for at least 4 cm
• SVT of the small saphenous vein for at least 4 cm
• Collateral SVT of the large saphenous vein of the thigh for at least 4cm

Exclusion Criteria:

• SVT of the grand saphenous vein reaching the saphenofemoral cross (within 3 cm)
• SVT of the small saphenous vein reaching the saphenopopliteal cross
• Documented proximal or distal DVT or pulmonary embolism
• SVT secondary to sclerotherapy
• Pregnancy and puerperium
• uncontrolled arterial hypertension (Systolic pressure > 180 mmHg and diastolic pressure > 110 mmHg)
• Active peptic ulcer
• Bacterial endocarditis
• Stroke in the previous 3 months
• Haemorrhagic diathesis
• Thrombocytopenia (platelets < 100,000/ µL)
• Hypersensitivity to heparin or history of thrombocytopenia induced by heparin
• Creatinine > 2 mg% (> 180 µmol/L)
• Heparin therapy (any dose) or anticoagulant therapy for longer than the previous 72 hours
• In-hospital development of SVT
• Previous saphenectomy by any method
• Surgery in the previous 30 days
• Serious liver disease
• Use of dextran, mannitol, thrombolytic treatment, chronic use of NSAID and cortisone-based drugs.
• Active cancer or under chemotherapy or radiotherapy
• Thrombectomy of superficial vein involved
• Refusal to give informed consent